The U.S. Pat. No. 6,599,284 to Faour discloses an osmotic device comprising an active agent and at least one excipient in the core, a semipermeable membrane surrounding the core and comprising a preformed passageway that increases in size during use and an optional scored region of the membrane adjacent the passageway. The preformed passageway is larger after use than it is prior to use of the osmotic device, and the internal pressure of the device increases during use causing a membrane edge defining the passageway to rupture.
U.S. Pregrant Publication No. 2005/0008702 to Faour and Vergez discloses a coated controlled release device, wherein the coating surrounding the core of the device ruptures forming a second passageway during use, due to a buildup of internal pressure, thereby allowing controlled delivery of an active substance contained in the core of the device to an environment of use.
The benefits provided by the rupturing devices disclosed in the U.S. Pat. No. 6,599,284 and the U.S. Pregrant Publication No. 2005/0008702 include: 1) approximately complete delivery of the active substance contained in the core; 2) an increased release rate of active substance during use as the second passageway permits additional contents of the core to be released more quickly than would occur through just the preformed passageway alone; and 3) enablement of the release of large particle size and/or generally insoluble active agents.
Osmotic devices containing a layer between the membrane and the interior compartment have been disclosed in the art to provide means for a variety of purposes, e.g. for easy control of the depth of penetration of a laser beam during formation of at least one exit orifice in a dosage form (U.S. Pat. No. 7,011,850 and Pregrant Publication No. 20050220879, both to Geerke); to promote the flow between the semipermeable wall and the drug layers (U.S. Pat. No. 6,368,626 to Bhatt, et al.); to protect a formulation comprising a drug and to increase the fluid-transmission rate into the dosage form to maintain the linear drug release over time (U.S. Pat. No. 6,210,712 to Edgren, et al.); to delay the release of the drug from the core (U.S. Pat. No. 6,764,697, No. 6,146,662 and No. 5,190,765, all to Jao, et al., U.S. Pat. No. 5,141,752, No. 4,986,987 and No. 4,948,592, all to Ayer, and U.S. Pat. No. 4,904,474 to Theeuwes); to provide protection for an antiepileptic drug from the pH of 1 to 8 of the gastrointestinal environment and to give the wall support against the stress and the strain of a fluid moving gastrointestinal tract (U.S. Pat. No. 5,876,750 to Jao, et al.); as an osmotic layer comprising hydrophilic polymer having a molecular weight of about 1,000,000 to about 15,000,000 (U.S. Pregrant Publication No. 20050220879 to Geerke); as a flow-promoting layer that facilitates release of drug from the dosage forms of the invention by reducing the frictional forces between the semipermeable wall and the outer surface of the drug layer, thus allowing for more complete delivery of drug from the device (U.S. Pregrant Publications No. 20050136113 to Bhatt, et al., No. 20060251721, No. 20050158382, and No. 20050089570, all to Cruz, et al., No. 20050260264 to Edgren, et al., and No. 20050208132 to Sathyan, et al.)
It has now been found that the variability in the release profile of a controlled release drug delivery device comprising a semipermeable membrane that ruptures during use can be restricted by adding a subcoat between the core and the semipermeable membrane.